1. Field of the Invention
The present invention relates to the field of semiconductor techniques, and particularly, to a semiconductor device.
2. Description of the Related Art
In modern semiconductor techniques, PMOS (P-channel Metal-Oxide-Semiconductor Field-effect Transistor) transistors work with negative bias voltage over a long term, which may lead to changes in electronic parameters of PMOS transistors, PMOS transistor degradation, or even cause failures. For example, in modern CMOS (Complementary Metal oxide Semiconductor) techniques, the NBTI (Negative Bias Temperature Instability) effect of PMOS transistors is a problem of primarily concern in terms of reliability.
The NBTI effect refers to the degradation of a series of electronic parameters at a high temperature due to the negative gate voltage applied to PMOS transistors. The creation of the NBTI effect mainly relates to the generation of positive charges and Passivation, that is, the generation of interface trapped charges and fixed oxide charges and the diffusion of diffusive materials; hydrogen and moisture are two major substances that can cause NBTI. Traditionally, the creation of NBTI may contribute to the fact that inversion layer holes are thermally excited under a high temperature and a negative bias voltage applied to a PMOS transistor and tunnel to the interface of Si/SiO2. Because there are a lot of Si—H bonds at the interface, the thermally excited holes react with Si—H bonds to produce H atoms, leaving dangling bonds at the interface. Due to the instability of H atoms, two H atoms may combine with each other, released in the form of hydrogen molecules, leading to negative threshold voltage shift.
Thus, the NBTI effect can cause issues, such as the rise of gate current, negative threshold voltage shifting after a long term of work, for PMOS transistors.